Abstract - This paper discusses the phenomenon of nutritional flushing in
ewes whereby increased nutrition stimulates folliculogenesis and ovulation
rate. In addition the paper reviews recent findings on the effects of
increased levels of nutrition on the blood concentrations of reproductive
and metabolic hormones in the ewe and some of the intraovarian changes that
take place in response to nutritional stimulation. Finally, in the paper, we
propose a model of the physiological mechanism for the nutritional
stimulation of folliculogenesis and we review how closely the model fits
recent published and unpublished evidence examining the mechanism of
flushing. Nutritional stimulation alters the blood concentrations of some
metabolic hormones. By using short-term models of nutritional flushing, we
have shown that as the blood concentrations of insulin and leptin increase
that of growth hormone decreases while that of IGF-I appears unaffected by
the nutritional flushing. Nutritional flushing also alters the blood
concentrations of some reproductive hormones. Again, using the same model,
we have shown that there is a transient increase in FSH and a decrease in
oestradiol concentrations in the blood. The changes in oestradiol are
particularly evident in the follicular phase of the oestrous cycle. In the
ovary, the effect of nutrition is to stimulate folliculogenesis. These
changes are associated with intra-follicular alterations in the
insulin-glucose, IGF and leptin metabolic systems. The stimulation of these
intra-follicular systems leads to a suppression in follicular oestradiol
production. The consequence of these direct actions on the follicle is a
reduced negative feedback to the hypothalamic-pituitary system and increased
FSH secretion that leads to a stimulation of folliculogenesis.